CVE-2026-63828 Details
Description
In the Linux kernel, the following vulnerability has been resolved: apparmor: mediate the implicit connect of TCP fast open sendmsg sendmsg()/sendto() with MSG_FASTOPEN is a combination of connect(2) and write(2): it opens the connection in the SYN. apparmor_socket_sendmsg() only checks AA_MAY_SEND, so a profile that grants send but denies connect lets a confined task open an outbound TCP/MPTCP connection that connect(2) would have refused, bypassing connect mediation. Mediate the implicit connect when MSG_FASTOPEN is set and a destination is supplied. Add it to apparmor_socket_sendmsg() (not the shared aa_sock_msg_perm() helper, which recvmsg also uses) and call aa_sk_perm() directly, mirroring the selinux and tomoyo fixes. sk_is_tcp() does not cover MPTCP fast open, so the SOCK_STREAM/IPPROTO_MPTCP arm is explicit.
A vulnerability in the Linux kernel's AppArmor security module allows a confined task to bypass connection mediation for outbound TCP connections using Fast Open. This issue arises because the AppArmor socket send message function only verifies the permission to send data, not to establish a connection. As a result, a profile that permits sending but denies connecting can exploit this oversight, particularly with TCP or Multipath TCP (MPTCP) connections. The vulnerability affects several versions of the Linux kernel.
Users can update to the latest version of the Linux kernel where this vulnerability has been addressed. Instructions for updating the kernel can be found in the official Linux documentation or through the package manager for your Linux distribution.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
No SSVC data is available for this CVE.
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Weakness Enumeration
No weakness enumeration is available for this CVE.
Affected Products
No affected product data is available for this CVE.
Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Aug 17, 2026 | CVE Modified | kernel.org |
| Jul 24, 2026 | CVE Modified | kernel.org |
| Jul 20, 2026 | CVE Modified | kernel.org |
| Jul 19, 2026 | New CVE Received | kernel.org |